1. Field of the Invention
The present invention relates to a semiconductor device. For example, the present invention relates to the structure of contacts connecting a transistor on a semiconductor substrate and an interconnect trench in an interlayer insulating film thereon.
2. Description of the Related Art
The conventional method of manufacturing contacts and interconnect (wiring) layers will be described below with reference to FIG. 14. First, a contact hole 103 is formed in an interlayer insulating film 102 on a semiconductor substrate 101. The contact hole 103 has a bottom portion reaching the semiconductor substrate 101. The contact hole 103 is filled with conductive materials via an adhesion layer 104 using a blanket CVD (chemical vapor deposition) process. The adhesion layer 104 has a function of providing preferable adhesion of materials filled in the contact hole 103 with the sidewall thereof when the CVD process is carried out. Extra conductive materials on the interlayer insulating film 102 are removed using CMP (chemical mechanical polishing), and thereby, a contact plug 105 is formed. An interlayer insulating film 107 having an interconnect trench 106 connected with the contact plug 105 is formed on the interlayer insulating film 102. Thereafter, the interconnect trench 106 is filled with a conductive film via a barrier metal 108.
Recently, with the scale-down of semiconductor devices, the aspect ratio of the contact hole 103 increases. For this reason, the following phenomena take place when the contact hole 103 is filled with conductive materials using blanket CVD. First, according to blanket CVD, the conductive material film uniformly grows from the side of the contact hole 103. For this reason, if the contact hole 103 has a defective shape (e.g., the diameter of hole opening is smaller than that of other portions), the opening of the contact hole 103 is closed before the contact hole 103 is filled. As a result, an empty space called a seam (void) 109 is formed in the contact hole 103. Secondary, if tungsten (W) is used as the material of the contact plug 105, the interface of W deposited from both sides of the contact hole 103 is formed with the empty space because W has a coarse surface.
The seam 109 is formed in the contact hole 103; as a result, the seam 109 opens as seen from FIG. 14 in the process of removing extra W by CMP or the RIE (reactive ion etching) process for forming the interconnect trench 106. Consequently, the barrier metal 108 is not continuously formed in the hole opening of the seam 109; for this reason, a broken portion is formed. If the interconnect trench 106 is filled with interconnect conductive film in a state that a broken portion is formed, the following problem arises. Electro-migration resistance is reduced on the basis of the broken portion; as a result, desired reliability is not obtained.
The adhesion layer 104 is employed when W is used as the material of the contact plug 105; in this case, the adhesion layer 104 has a specific resistance smaller than W. For this reason, when the diameter of the contact hole 103 become gradually small, the ratio of the adhesion layer 104 occupying the cross-sectional area of the contact hole 103 becomes high. As a result, the resistance of the contact plug 105 increases.